The end of tonight's episode saw the DC TV heroes celebrating, with Supergirl back to her Kara Danvers self. As she walks away, Ray Palmer (Brandon Routh) says she looks a lot like his cousin.
This is a nod to Brandon Routh playing Superman in 2006 with Superman Returns (as Superman and Supergirl are cousins).
Producer Marc Guggenheim offered the following to IGN about the Superman reference:
Basically, it’s sort of like last year on Legends we did the Prison Break [reference], it was like, I said to the writers, ‘If we don’t make a Prison Break joke here with Wentworth [Miller], we’re not doing our jobs.’ I was like, “If we have Brandon [Routh] and Melissa [Benoist] share the screen and we don’t make some sort of joke like that, we’re not doing our job.’ The truth is, that joke existed on Arrow originally and then a certain scene got cut so then I moved it over to Legends; I just kept moving it back and forth. I’m like, ‘I’m getting it in one of these episodes.